Kinetics and Catalysis最新文献

Nickel oxide (NiO) nanoparticles were synthesized using four different methods: microwave co-precipitation (MCP), solution combustion synthesis (SCS), direct nitrate calcination (DNC), and the sol-gel process (SGP), incorporating organic additives such as glucose and fructose. X-ray diffraction and Raman spectroscopy analyses revealed that the NiO nanoparticles formed a face-centered cubic phase characterized by Ni–O bond stretching. The SCS method produced NiO nanoparticles with higher lattice strain, smaller crystallite size, and an increased facet ratio ({110}) compared to the other methods. Transmission electron microscopy indicated that the order of nano-agglomeration size for the NiO nanoparticles was DNC > MCP > SGP > SCS. The NiO nanoparticles synthesized via SCS, SGP and MCP exhibited irregular hexagonal shapes. Among the synthesized nanoparticles, those produced by the SCS method demonstrated the highest catalytic activity (T₅₀ = 478°C), followed by DNC (T₅₀ = 492°C), MCP (T₅₀ = 495°C), and SGP (T₅₀ = 538°C). A kinetic study was conducted to evaluate key parameters, including activation energy, preexponential factor, and reaction model. The experimental curves of soot conversion were compared with theoretical curves derived from the evaluated kinetic parameters. The NiO nanoparticles synthesized via SCS exhibited the highest kinetic activity with the enhanced reaction rate at lower temperatures.

Photocatalytic reduction of CO₂ is one of the promising strategies for synthesising valuable organic compounds and solving both energy and environmental problems. In the present work, NiO/Ni/g-C₃N₄ photocatalysts were synthesised. Initially, g-C₃N₄ was prepared by calcination of melamine and urea and then modified by photodeposition of a NiO/Ni co-catalyst on its surface. The structure of the photocatalysts was confirmed by X-ray phase analysis, UV–Vis diffuse reflection spectroscopy, and high-resolution transmission electron microscopy. The highest activity in the reaction of photocatalytic CO₂ reduction was demonstrated by 2 wt % (NiO/Ni)/g-C₃N₄ and 3 wt % (NiO/Ni)/g-C₃N₄, equal to 13.2 and 12.4 μmol g^–1 h^–1, respectively. It is worth noting that in this case, an almost 3-fold increase in the reaction rate was achieved compared to the pristine g-C₃N₄. The deposition of NiO/Ni on g-C₃N₄ solves two fundamental problems: adsorption of CO₂ and separation of photogenerated electrons and holes. The present work demonstrates an approach to the synthesis of active catalysts, in particular an approach to design a hybrid NiO/Ni co-catalyst for efficient photocatalytic CO₂ conversion.

In this work, nanosized titanium dioxide was synthesized and the effect of acidity of the medium on its structure and properties was studied. Photocatalysts were prepared by a sol–gel method from titanium tetrabutoxide, ethyl alcohol, and water in a ratio of 1 : 1 : 4 at different pH (3, 7, and 9). Powder modification was carried out by annealing in air at 150–750°C. The structure of the synthesized initial and modified annealed photocatalysts was studied by XRD analysis and the phase ratios were determined. An analysis of the experimental data showed that the acidity of the medium did not have a strong influence on the phase formation and phase ratio of the resulting photocatalysts. It was found that the annealing temperature had a greater effect on the structure and properties: the phase ratio, coherent scattering regions (CSR), and specific surface area were changed. The powders prepared in this work had high specific surface area and complicated phase composition, which made them promising for photocatalysis, in particular, in a hydrogen evolution reaction.

A model reaction of radical chain oxidation of methyl oleate was used to study natural compounds for antioxidant activity. Secondary peroxyl radicals were generated by controlled initiated lipid oxidation. The system was used to evaluate the antioxidant activity of natural oils obtained by extracting crushed seeds of the medicinal plants evening primrose and borage. The effective rate constant of methyl oleate peroxyl radicals with inhibitors contained in the oils was measured. The concentration of antioxidants was found and the qualitative composition of the antioxidants was suggested.

In recent decades, with population growth and rapid industrialization, the contamination of water resources has become a pressing concern, with organic pollutants, heavy metals, and other complex compounds playing a significant role. Consequently, the development of novel materials that can harness natural energy and employ it for wastewater treatment represents a crucial objective. In this study, a PVDF/BaTiO₃ composite membrane was synthesized via the electrospinning method. The synthesized materials were subjected to investigation by means of scanning electron microscopy (SEM), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The incorporation of BaTiO₃ resulted in a notable reduction in fiber diameter, with a 2.9-fold decrease observed. Fourier transform infrared spectroscopy (FTIR) revealed that the β-phase fraction decreased from 87.3 to 74.3%, while the γ‑polymorph increased from 10.7 to 20.9%. The catalytic properties of the composite were investigated by subjecting it to the decomposition of methylene blue. The photocatalytic process yielded 61% decomposition, the piezocatalytic process yielded 77% decomposition, and the piezophotocatalytic process (simultaneous exposure to ultrasound and UV-visible light) yielded 98% decomposition in 60 min. The synergetic effect of the two processes was 33.7%. The oxidation mechanism in piezo- and piezophotocatalysis is based on the action of hydroxyl radicals (^•OH). Experimental evidence has demonstrated that the membrane generates voltages more than 20 V under ultrasound conditions, thereby promoting silver reduction. These materials have the potential to contribute significantly to the degradation of dyes and the purification of aqueous media, thereby facilitating the development of more efficient and sustainable water treatment methods.

It has been found that the activity of the zeolite (Fe-Beta) and oxide (V₂O₅–WO₃/Al₂O₃) catalysts in the selective catalytic reduction (SCR) of NO by NH₃ can be significantly improved in the temperature range of 100–250°C by introducing ozone into the gas stream entering the catalyst. The study of the temperature dependences of the reaction product composition shows that for the oxide catalyst the increase in NO_x conversion occurs due to NO_x reduction via “fast” SCR pathway, whereas for the zeolite catalyst the NO₂-SCR pathway also makes a significant contribution.

This paper shows the results of a study on hydrogen peroxide formation in aqueous suspensions of anatase or rutile titanium dioxide with palladium particles deposited on its surface under the action of UV radiation. The formation of peroxide species on the photocatalyst surface was confirmed by IR spectroscopy, and the quantitative determination of hydrogen peroxide in solution was carried out by a colorimetric method using a special reagent containing peroxidase. To determine the pathway of peroxide compound formation, the effect of the composition of the gas phase (Ar, O₂) and liquid (water or aqueous methanol solution) on the accumulation of H₂O₂ was studied. The Pd-modified photocatalyst based on rutile exhibited significantly higher activity compared to that of the anatase-based photocatalyst. In both cases, the highest yield of H₂O₂ was achieved due to oxygen photoreduction upon the addition of methanol as an additional electron donor, which provided an increase in the rate of hole transfer as a rate-limiting step.

In this work, graphitic carbon nitride samples modified simultaneously with bromine and iodine were prepared using a two-step synthesis method. The composition and physicochemical properties of the prepared samples were investigated by a set of physicochemical methods including X-ray diffraction (XRD) analysis, low-temperature nitrogen adsorption, diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), thermal analysis, cyclic voltammetry, and impedance spectroscopy. The catalytic properties of the synthesized samples were measured under the illumination of an aqueous alkaline solution of triethanolamine. The samples simultaneously modified with bromine and iodine showed higher catalytic activity compared to the samples modified with bromine or iodine alone. A maximum catalytic activity of 2400 μmol h^–1 g^–1 was obtained in the presence of a 0.5% Pt/0.4Br–0.1I sample. Cyclic experiments showed that the samples modified with bromine or iodine alone showed higher photostability, as a result of which modification with one halogen allows the process of photocatalytic hydrogen evolution to be carried out with higher efficiency.

Solution combustion synthesis (SCS) is a powerful route for synthesizing a wide range of nanostructures. The fine adjustment of the experimental parameters (fuel type, fuel/oxidizer ratio, pretreatment temperature, etc.) plays a crucial role in controlling the structural as well as the textural features of the resulting nanomaterial. In this study, we investigate the synthesis of silver nanoparticles (Ag NPs) using the combustion method with glycine as a fuel. The calcination of the silver nitrate/glycine precursor was performed over a temperature range of 150–600°C. The obtained Ag NPs were characterized by XRD, FTIR, TEM, and XPS techniques. XRD diffraction patterns revealed that the development of Ag NPs started at 150°C. FTIR spectroscopy confirmed the presence of various functional groups in the calcined samples. TEM images revealed that increasing the temperature from 200 to 600°C resulted in a morphology change from accumulated spheres into inter-welded capsules. XPS analysis detected Ag, O, and C at the surface of the prepared Ag NPs. NaBH₄ hydrolysis, at the temperature range of 30–50°C, was chosen for evaluating the activity of the prepared Ag NPs. It was found that the activity increased with increasing reaction temperature, with the optimal activity exhibited by the sample calcined at 400°C. The investigation was extended to check the effect of various parameters including NaBH₄ weight, alkalinity, and recycling on the activity of the optimal catalyst.